Yes, this is normal. OpenID is specific to site domain name in some cases, for example Google OpenID (google is even making openid string dependent on subdomain)

This has an implication that if you change your site domain name or subdomain, some users won't be able to re-use their openid. They will be able to recover the account via email though (if they give real email the first time they register).

Yes, this is normal. In some cases (but not all cases) OpenID is specific to site domain name in some cases, name, for example Google OpenID (google is even making openid string dependent on subdomain)

This has an implication that if you change your site domain name or subdomain, some users won't be able to re-use their openid. They will be able to recover the account via email though (if they give real email the first time they register).

Yes, this is normal. In some cases (but not all cases) OpenID is specific to the domain name of the site domain name, for like askbot. For example Google OpenID (google is like that, they even making make openid string dependent on subdomain)the subdomain.

This has an implication that if you change your site domain name or subdomain, some users won't be able to re-use their openid. They will be able to recover the account via email though (if they give real email the first time they register).